Meaning of Flutter map Function-CodePudding

Please I'm need clarification on what the Map funtion and spread function does in flutter.

...(questions[questionIndex]['answers'] as List<String>).map((answer) {
    return Answer(selectHandler: answerQuestion, answerText: answer);}).toList()

In the code above, I have Question map with keys and values, but the transformation process of the list to widget using map function with spread indicated by three dots, is what I need clarification on. Please someone help me explain to me. Thanks.

Also is there any other recommendation on transforming list to wiidget without using map function?

CodePudding user response：

the spread operation let you combine a List element inside another List, it's like you say: "merge the elements of that spread list into the main list".

example :

list<int> list1 = [1, 2, 3];
list<int> list2 = [4, 5, 6];
list<int> margeOfElementsOfLists = [...list1, ...list2];

print(margeOfElementsOfLists); // [1,2,3,4,5,6]

in the other hand, the map method is not related directly to the Map object in dart. it gives you the ability to get a copy of the original list with executing a kind of function on all elements, taking the previous list :

print(margeOfElementsOfLists.map((number) => number *2).toList()); // [2,4,6,8,10,12]

so in your case, it's like you're saying, for all elements, create a widget that takes the answer as property and makes from it an Answer widget, then merge the elements of that list inside of the main List, which can be the children List of a Row or Column

CodePudding user response：

I am beginner in flutter...so far I have noticed that map is easy to use than other looping...

I had a created a demo regarding it

here it is ...if it might help u

class MyApp extends StatelessWidget {
   MyApp({Key? key}) : super(key: key);

   List<int> numbers = [3, 5, 2, 4, 5, 6, 2];

  List<Widget> int_to_widgetlist() {
    // using map u can code as per following
    //return numbers.map((e) => Text(e.toString())).toList();

    // or u can use for loop or any other loop
    List<Widget> widgetlist = [];
    for (int x = 0; x < numbers.length; x  ) {
      widgetlist.add(Text(numbers[x].toString()));
    }
    return widgetlist;
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Column(
          children: int_to_widgetlist(),
        ),
      ),
    );
  }
}

and about spread operator its is like

var list = [1, 2, 3];
var list2 = [0, ...list];